1. Field of the Invention
The present invention relates to a device for locking rotation of an eccentric bearing used in a compression ratio changing device for an internal combustion engine. More particularly, the present invention relates to a device for locking the rotation of the eccentric bearing at every compression ratio except when the compression ratio is exchanged.
2. Description of the Prior Art
A compression ratio changing device using an eccentric bearing is generally known as taught by Japanese Utility Model Publications No. SHO 58-137832, No. SHO 61-198531, No. SHO 61-192533, and No. SHO 61-183433. As described therein, the eccentric bearing has a cylindrical outside surface and a cylindrical inside surface eccentric with respect to the outside surface, and the eccentric bearing is rotatably interposed between a connecting rod and a piston-pin extending through a small end hole of the connecting rod. The rotation of the eccentric bearing changes a relative position of a piston with respect to the connecting rod and, as a result, changes the compression ratio of the internal combustion engine. The rotation of the eccentric bearing relative to the connecting rod is locked/unlocked by moving a single lock-pin which is slidably interposed in a single lock-pin hole formed in the connecting rod into/from a single lock hole formed in the eccentric bearing in the radial direction of the small end hole of the connecting rod. The lock hole is formed in the eccentric bearing at such a position that the lock hole can receive one end portion of the lock-pin when the thickest wall portion of the eccentric bearing comes to its lowest position with respect to the rotational axis of the eccentric bearing.
When engine loads are low or medium and, accordingly, a high compression ratio is required, the lock-pin is biased toward the eccentric bearing by pressurized oil which is supplied to the lock-pin hole, and the lock-pin engages with the lock hole to lock the rotation of the eccentric bearing at a high compression ratio. On the other hand, when engine loads are high and, accordingly, a low compression ratio is required for the purpose of preventing knocking of the engine, the lock-pin is moved away from the eccentric bearing and disengages with the lock hole to unlock the rotation of the eccentric bearing. When unlocked, the eccentric bearing can rotate freely receiving moments which are produced by the loads from the piston and the arm of eccentricity of the eccentric bearing. The eccentric bearing naturally takes a low compression ratio position where the thinnest wall portion of the eccentric bearing comes to its lowest position with respect to the rotational axis of the eccentric bearing.
In such a compression ratio changing device where the low compression ratio is obtained through unlocking the rotation of the eccentric bearing, there are the following disadvantages:
Firstly, because the rotation of the eccentric bearing changes the sway-movement center of the piston relative to the connecting rod, the piston is liable to cause a slap movement with respect to a cylinder bore, and the slap noises become severe in the low compression ratio state.
Secondly, because the eccentric bearing -continues to rotate at high speeds during the low compression ratio state, the lock-pin collides with the surface of the lock hole of the eccentric bearing at high speeds when the compression ratio is exchanged from the low compression ratio to a high compression ratio. This decreases the durability of the assembly of the lock-pin and the eccentric bearing.
Thirdly, because the eccentric bearing continues to rotate during the low compression ratio state, the sliding surfaces including the outside surface of the eccentric bearing and the inside surface of the small end hole of the connecting rod are liable to be severely abrased, and the rotation of the eccentric bearing is liable to be deteriorated.